<local:FeedViewModel
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"       
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:RssReader" 
    FeedName="Test">
    <local:FeedViewModel.Items>
        <local:FeedItemViewModel 
            Description="description1" 
            Title="Post1 This is very  long text longer than can be seen on the screen" 
            Url="http://www.web.com" />
        <local:FeedItemViewModel 
            Description="description2" 
            Title="Post2 This is very  long text longer than can be seen on the screen" 
            Url="http://www.web.com" />
        <local:FeedItemViewModel 
            Description="description2" 
            Title="Post3 This is very  long text longer than can be seen on the screen" 
            Url="http://www.web.com" />
     </local:FeedViewModel.Items>  
</local:FeedViewModel>